[Feature]: 建议默认tex编译器替换为xelatex

### Feature Request | 功能请求

本地部署使用论文翻译时经常有”由于最为关键的转化PDF编译失败, 将根据报错信息修正tex源文件并重试“的问题，这是因为pdflatex 本身对字体的支持有限，尽管 pdflatex 能通过一些宏包支持中文，但需要手动导入字体，排版效果和功能上通常不如 xelatex 或 lualatex 来得简便和完美。建议还是使用 xelatex 或 lualatex，更好支持 fontspec 或 ctex 宏包。

Start by locating the PDF/LaTeX compilation entry point and identify where pdflatex is selected as the default. Verify the behavior with the paper-translation workflow; done means the default compiler is xelatex and generated PDFs compile successfully with the intended font support.

Written by the indexing model from the issue text.